1. Field of the Invention
The present invention relates to a positional deviation correction pattern, a method of forming a positional deviation correction pattern, and an image forming apparatus.
2. Description of the Related Art
In various image forming apparatuses such as an electrophotographic apparatus and an inkjet recording apparatus, it is important to form an image at a correct position with respect to an image bearer such as a photoconductor, an intermediate transfer body, and a recording sheet without a deviation.
Japanese Laid-open Patent Publication No. H01-112266 discloses an image forming apparatus in which a pattern image for a positional deviation correction is formed on an image bearer to correct a positional deviation of an image, and a position of the pattern image formed is detected by a reflective photo-sensor. In the image forming apparatus, the amount of deviation between an actual drawing position and an ideal drawing position of the image in a main-scanning direction is calculated from a length of the pattern image in the sub-scanning direction, which is detected by the photo-sensor. The image forming apparatus corrects a main-scanning direction position of the image by adjusting a drawing position of the image based on the amount of deviation calculated.
In a case where the pattern image for correction is detected by the reflective photo-sensor, a threshold is set with respect to an output voltage of the photo-sensor. For example, when a voltage value lower than the threshold is output, the image forming apparatus determines that the pattern image for correction of the positional deviation is detected. However, there is an error between timing at which an edge portion of the pattern image passes through the photo-sensor, and timing at which the photo-sensor detects the edge portion of the pattern image. This error varies in accordance with an environment temperature when the pattern image is detected, a density of the pattern image, a color of the pattern image, a contamination degree of a light-receiving unit of the photo-sensor, and the like. When an output error of the photo-sensor varies, there is a problem in that detection accuracy of the length of the pattern image in the sub-scanning direction, and positional deviation correction accuracy decreases.
Therefore, there is a need for a positional deviation correction pattern by which a positional deviation of an image can be detected with accuracy in a simple configuration, a method of forming the positional deviation correction pattern, and an image forming apparatus that uses the positional deviation correction pattern.